The present invention relates to a new and improved arrangement of strand guide rolls mounted coaxially and neighbouring one another in a continuous casting installation for casting steel slabs.
The guide rolls of continuous casting installations are subjected, during each revolution of the rolls, to a high mechanical alternating load by virtue of the ferrostatic pressure which is effective at the strand shell or skin. This high mechanical alternating load can exceed 100 tons per roll in the case of slab casting installations. An additional loading of the rolls occurs because of the shock-like temperature increase of the roll surface during each contact of the rolls with the hot strand. Depending upon the strength of the roll material these mechanical and thermal loads require a predetermined roll diameter.
The momentarily employed roll diameter requires a certain minimum spacing between the rolls, and thus, determines the size of the unsupported surface between successive rolls. The mutual dependency between the permissable roll loading, the strand width, the strand shell or skin thickness, the ferrostatic pressure, the roll diameter and the spacing between successive rolls, when casting large sectional shapes or formats, limits the casting speed, since deleterious bowing-out and metal break-out must be avoided. Strands having a width of, for instance, in excess of 2 meters and at least 150 mm thickness require either expensive roller apron frameworks or in the case of vertical or curved or arc-type roller aprons can only be cast with relatively short liquid core and only with relatively low casting speeds.
In order to render possible casting of strands of greater width at increased casting speeds, it is already known in this technology to use, in place of continuous guide rolls, multiply supported guide rolls. A prior art strand guide roll consists of a number of roll sections, whose roll journals at one side are threaded into recesses of the neighbouring roll section, and between the roll sections there is provided in each case a support bearing. Extending through the roll sections is a cooling channel. Significant in this regard is German Pat. No. 2,420,514, published July 10, 1975. With this constructionally complicated strand guide roll the assembly and the exchange of the rolls is cumbersome and time-consuming. Since tthe connection journals are exposed to intensive bending loads the roll sections can not be appreciably extended in length in order to reduce the bearing locations. A further drawback of such guide roll is that at the connection locations between the rolls and journals there is hindered heat transfer, so that there is not ensured for uniform cooling throughout the roll length.
Also in British Pat. No. 1,565,845, published Apr. 23, 1980, there is disclosed a roller apron or strand guide arrangement, wherein over the strand width there are coaxially mounted in each case two guide rolls. With this economically favorable construction it is possible to assemble and dismantle the guide rolls more quickly. However, what is disadvantageous with this design is that in the case of a strand which bears at one side only at one roll the coaxially neighbouring other roll remains stationary and because of the one-sided overheating by the strand is extensively thermally loaded. Consequently, at this region there is promoted the formation of heat cracks and notwithstanding cooling the roll is bent-through in the direction of the strand. With renewed contact with the strand the bearings are markedly loaded. The untrue running of the guide rolls can lead to an irregular supporting of the strand, and thus, to strand defects or flaws. Moreover, the cooling system between two neighbouring rolls is complicated.
Further constructions of roller aprons and guide rolls used in continuous casting installations are exemplified by U.S. Pat. No. 4,071,073, granted Jan. 31, 1978 and U.S. Pat. No. 4,222,433, granted Sept. 16, 1980.